Vulnerability · Published Oct 26, 2026 · Assigned by EEF
CVE-2026-110499Client-chosen HPACK encoder table size is applied uncapped, growing per-connection state with every response in Bandit
High 8.7
In plain English
A high-severity resource allocation without limits in bandit from mtrudel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities).
Official description
Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to grow per-connection memory and CPU cost without bound via a large SETTINGS_HEADER_TABLE_SIZE. Bandit resizes its HPACK encoder table to whatever size the client advertises, up to 2^32-1 bytes, and indexes response headers into it. Because responses carry distinct values such as date or content-length, nothing is evicted and the table grows with every response for the life of the connection, while each lookup scans it linearly. The SETTINGS handling in Bandit.HTTP2.Connection (lib/bandit/http2/connection.ex) passes remote_settings.header_table_size to HPAX.resize/2 with no server-side cap, and encode_headers encodes every response header as :store. Serving N responses on one connection therefore costs O(N²) CPU in the connection process. This issue affects bandit: from 0.3.6 before 1.14.0.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu:22.04:LTS | bandit | no fix listed | UBUNTU-CVE-2026-110499 |
| Ubuntu:24.04:LTS | bandit | no fix listed | UBUNTU-CVE-2026-110499 |
| Ubuntu:26.04:LTS | bandit | no fix listed | UBUNTU-CVE-2026-110499 |
| Ubuntu:26.10 | bandit | no fix listed | UBUNTU-CVE-2026-110499 |
Affected products (as reported)
Weakness: CWE-770 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
References
- Client-chosen HPACK encoder table size is applied uncapped, growing per-connection state with every response in Bandit vendor-advisory, related
- EEF CNA record for CVE-2026-110499 related
- OSV record EEF-CVE-2026-110499 related
- Introducing commit 0e68313 in mtrudel/bandit related
- Fix commit 220b9df in mtrudel/bandit patch